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Aquifer texture data describing the Long Island aquifer system

January 2, 2022

The data contained in this data release support USGS Scientific Investigations Report 2020-5023, "Distribution of selected hydrogeologic characteristics of the upper glacial and Magothy aquifers, Long Island, New York" (Walter and Finkelstein, 2020).

This data release contains estimates of aquifer texture describing the Long Island aquifer system. These estimates in total can be considered a model of aquifer texture describing unconsolidated sediments in the following principal units: 1) Upper glacial aquifer, 2) Jameco aquifer, 3) Monmouth Greensand confining unit, and 4) Magothy aquifer. The Lloyd aquifer, a major aquifer on Long Island, is not included in the model due to a lack of available data. Aquifer texture characteristics estimated include: 1) horizontal hydraulic conductivity, 2) vertical hydraulic conductivity, and 3) the probabilities of occurrence of a) clay/silt, b) lignite, and c) pyrite. Probabilities of lignite and pyrite occurrence are limited to the Magothy aquifer and Monmouth Greensand.

The aquifer texture was estimated using lithologic descriptions obtained from 1,769 boreholes across Long Island using methods similar to Arihood (2008), Faunt and others (2010), and Walter and others (2018). In total, 36,364 unique lithologic descriptions from the boreholes were compiled and categorized into 45 separate USGS Ground-Water Site-Inventory (GWSI) System codes (USGS, 2004). The boreholes used to derive the texture model targeted the deepest hole within each 1-mi2 cell of a Long Island-wide grid. The 45 GWSI codes were further aggregated into 14 categories: 7 each for glacial and Cretaceous aquifer sediments. Each of the 14 categories were assigned estimated values of horizontal and vertical conductivity based on previous investigations and literature values for the Long Island aquifer system (Smolensky and others, 1989; Lindner and Reilly, 1983; McClymonds and Franke, 1972; Franke and Getzen, 1976) and similar hydrogeologic environments on the coastal plain of Massachusetts (Barlow and Hess, 1993; Barlow, 1989; Masterson and Barlow, 1997; Masterson and others, 1998; Guswa and LeBlanc, 1985; Guswa and Londquist, 1976; LeBlanc and others, 1986; Walter and others, 1996).

Horizontal and vertical hydraulic conductivities were estimated for each of the 14 aggregated lithologic codes. Subsequent calculations were applied to these values to determine a thickness-weighted mean and geometric mean hydraulic conductivity for 10-foot intervals across Long Island. An ordinary kriging interpolation was performed on these points within each 10-foot interval to generate a set of grids, with a 500-foot resolution.

The probability of occurrence of clay, lignite, and pyrite was determined from binary variables assigned using keywords in the lithologic descriptions. Descriptions containing the appropriate keywords were assigned a probability of 1, while a value of 0 was assigned to those without the keywords. The mean probability of the occurrence of clay, lignite, and pyrite (represented as binary variables) was computed for each 10-foot interval for each borehole. Ultimately, a database of X, Y, and Z coordinates, estimates of horizontal and vertical hydraulic conductivity and the probability of occurrence of clay, lignite, and pyrite was assembled.

The results of this analysis are documented as two sets of comma-delimited text files that include the location and altitude of the center of each cell along with an estimated value of each textural characteristic. Spatial coordinates are in feet, relative to the NAD27 datum. The altitude is in feet, NAVD88 datum. Data describing the upper glacial aquifer is contained in the file named ‘Pleistocene_Sediments.txt’. Data for the Cretaceous sediments underlying the glacial aquifer, are broken into three separate text files (Cretaceous_Sediments_1, 2, and 3) due to their size.